NEW YORK (CNN/Money) - One baseball fan is betting an awful lot on Barry Bonds.

Seller Steven Williams is planning to donate a portion of the proceeds to charity.

An auction took place on Overstock.com (up $3.95 to $57.40, Research) for the baseball that the San Francisco Giants slugger hit to bring his career home run tally to 700.

A registered user bidding under the tag, "bomasterj," bought the ball for $804,129, according to the site. But the sale has yet to be finalized until payment has been received, and officials at Overstock declined to identify bomasterj.

"I think that it is outrageous. It is way more than the ball is worth," said Mike Heffner, president of Lelands.com, an auction house specializing in sports memorabilia. "If I were to appraise the ball, I would put it into the $100,000 to 200,000 bracket."

Lelands.com auctioned another famous Bonds ball in 2003 after the slugger hit 73 home runs in a single season. That ball went for "only" $517,500 but was sold to Todd McFarlane, the baseball collector who spent more than $3 million to buy Mark McGwire's 70th home run ball.

Heffner, however, freely admitted the McGwire ball wasn't worth "anywhere near that."

Should Bonds surpass Babe Ruth, currently number two on the career home run list at 714, the value of Bonds' 700th home run ball would drop dramatically, Heffner said.

"People are going to be looking forward," Heffner told CNN/Money. "Unless something tragic happens to Barry Bonds next year, he will break Babe Ruth's record at 714."

From there, Bonds will chase the big one: Hank Aaron's all-time career mark of 755. Again, assuming Bonds doesn't get injured, that record seems well within his reach, either in 2005 or the season following.

So what makes a fan bid $804,129 for a potentially worthless ball?

"Todd McFarlane knew that the [McGwire] ball wasn't worth $3 million when he bought it, but he got $3 million worth of press off of it," Heffner said. "So he was very smart in that area."

The ball is being sold by 26-year-old Steven Williams, who caught the ball at San Francisco's SBC Park on September 17, when Bonds became the first player in 31 years to join baseball's 700 club.

Williams says he is planning to use some of the money to buy a new car for his mother and to pay some of the legal fees he has incurred over a legal dispute involving ownership of the ball.

"I am not going to put myself in debt to hold on to the baseball," he says.

A portion of the proceeds, he adds, will go to Mothers Against Drunk Driving (MADD) and the Edgewood Center for Children and Families in San Francisco, a family counseling center.